1. Field of the Invention
The present invention relates generally to methods and apparatus for controlling the delivery of fuel to an internal combustion engine and, more particularly, to a method and apparatus for an intelligent fuel control system for optimizing the quantity of fuel delivered to an internal combustion engine and for minimizing errors caused by an engine's age, condition or fuel being utilized, based on past detected performance. Optimization of the fuel control process will allow for the best and most efficient operation of a catalytic converter.
2. Description of the Prior Art
Electronic fuel control systems are increasingly being used in internal combustion engines to precisely meter the amount of fuel required for varying engine requirements. Such systems vary the amount of fuel delivered for combustion in response to multiple system inputs including throttle angle, measured air intake, and the voltage output from the Heated Exhaust Gas Oxygen sensor (HEGO) while analyzing the exhaust gas produced by combustion of the air and fuel.
Electronic fuel control systems operate primarily to maintain the ratio of air and fuel at or near stoichiometry. Electronic fuel control systems operate in a variety of modes depending on engine conditions, such as starting, rapid acceleration, sudden deceleration, cruse and idles. One mode of operation which is of the most importance to us is closed-loop fuel control. Under closed loop control, the amount of fuel delivered is determined primarily by measuring the air entering the engine, calculating the appropriate fuel needs and then correcting the amount of fuel needed based on a voltage output from a HEGO. In this example, a HEGO sensor output with voltages between 0.45 Volts and 1.1 Volts is often considered "Rich", voltages between 0.0 and 0.45 are generally considered "lean". A sensor voltage output indicating a rich air/fuel mixture (an air/fuel ratio below stoichiometry) will cause the control system to decrease the amount of fuel being delivered. Conversely a HEGO voltage below a value indicating stoichiometry will cause the control system to increase the amount of fuel delivered to the engine.
Modern vehicle engines utilize a three-way catalytic converter to reduce unwanted by-products of combustion also known as regulated emissions. The catalytic converter has a finite number of active sites where the electromotive forces are optimum for a desired electrochemical reaction to take place. The number of active sites limit the mass quantity of reactants that the converter is able to process at any given time.
Maintenance of the ratio of air and fuel at or near stoichiometry is critical for efficient operation of the catalytic converter. In order to effect maximum conversion efficiency from a three way catalyst, discrete cyclical quantities of rich and lean exhaust gasses must be delivered to the catalyst. Occasional richer and leaner cycles of exhaust gasses must be utilized to clean some of the active sites which have been occupied (also known as poisoned) by chemical reactants which have been electro-chemically bonded to these sites. Balancing the excursions between rich and lean exhaust is important in ensuring that an adequate number of active sites in the converter are available for future conversion to take place. A lean air/fuel ratio will oxidize the active sites occupied by "rich" reactants such as carbon monoxide (CO) and Hydrocarbons (HC's), with "lean" reactants such as Oxygen (O2) and Oxides of Nitrogen (NOx). As the rich reactants are removed, the active sites are "charged" with lean reactants which will allow the ensuing rich excursion to reduce these reactants. In this manner, the catalytic converter will attain maximum conversion efficiencies. The magnitude and frequency of the rich/lean excursions should never be large enough to saturate the catalyst. A saturated catalyst is somewhat deactivated until many of the active sites can be cleaned of the occupying chemical or poison.
When altering the air/fuel ratio in response to the detected exhaust gas oxygen sensor voltage output, electronic fuel control systems known in the art respond in a predetermined way to a detected air/fuel ratio. Consequently, factors such as imprecision in the predetermined response, variations from engine to engine, variations in the fuel provided to the engine, aging of parts, and other characterized changes will cause changes in the performance and efficiency of the engine which will then suffer accordingly.
An example of an intelligent fuel control system is disclosed in U.S. Pat. No. 5,253,632, issued to Brooks. Brooks teaches an air/fuel mixture control system for an internal combustion engine in which a closed loop controller varies the air/fuel mixture in response to measurements of the oxygen level within the engine's exhaust emissions to achieve stoichemetry. The oxygen sensor produces a binary sensor signal indicative of either a rich or lean mixture. The controller responds to changes in the binary sensor signal by delivering fuel at a fixed rate until either the sensor responds by indication of an oxygen level change or a predicted transport delay interval expires. In the event the predicted interval expires before the sensor responds, the fixed rate of fuel delivery is adjusted in an effort to obtain the desired level change within the allotted interval. In the event that the level change is delayed beyond a set limit, the transport delay interval is enlarged. If the control system raises the fuel delivery rate above a predetermined rich limit, or below a predetermined lean limit, the base rate from which the initial rates are derived is increased or decreased respectively.
The shortcoming of the Brooks '632 reference is the teaching of the fuel injection wave form (in solid graphical representation) and the sensed oxygen level wave form (in phantom graphical representation) forever modulating in offset fashion from one another aside from momentary intersections at the desired stoichemetric level (represented by centerline 1.0). As is clearly illustrated, the peaks of the wave-shape illustrating the exhaust oxygen levels are delayed from the corresponding peaks of the fuel-intake waveshape, this offset resulting from the physical transport delays resulting from the air and fuel passing through the engine components up to the position of the sensor in the exhaust stream. Thus, the system of Brooks is forever hunting about for a stoichemetric level between the oxygen input and the fuel delivery rate and based only upon the original parameters existing prior to the first cycle of operation.